1. Field of the Invention
The present invention relates to a data use management system, a transmitting apparatus having a management function, a data use management method, and so on which are used for, for example, management of use of data which needs copyright protection.
2. Related Art of the Invention
In recent years, implementation of home networks, in which appliances are connected in a home to share information, has been pursued. In one form of a home network, a router is provided in a home. An AV server, which accumulates information contents, appliances including a personal computer (PC) and a digital television set are connected in a star configuration to the router. The router connects the network in the home to a network outside the home. The AV server in the home has the functions of temporarily storing various information contents obtained through the router from networks outside the home and information contents obtained from means other than networks, such as digital broadcasting, and transmitting stored information contents to an appliance when receiving a request from another appliance.
When data for which a copyright exists, e.g., new films, pay television programs and music, there is a need to protect copyrights. As an effective method of protecting copyrights, a method is known in which data which needs copyright protection is encrypted to limit use of the data.
For example, in a case where there is a need to copyright-protect audio-visual data (hereinafter referred to as AV data) when the AV data is used and transmitted, the AV data is encrypted before being transmitted. For example, the DTCP (Digital Transmission Content Protection) system was standardized as such a protection method.
The DTCP system has the function of performing authentication and the function of making a key ineffective. At the time of transmission of AV data, the DTCP system excludes unauthorized appliances, which have not been authenticated, and encrypts and transmits data which needs copyright protection. This inhibits use of AV data with unauthorized appliances. Copyright protection is achieved in this manner.
Use of AV data which needs copyright protection is ordinarily limited to personal use in homes. Therefore, there is also a need to limit the distribution of AV data from an AV server in a home to unspecified receiving apparatus outside the home.
In the DTCP system, when a transmitting apparatus is requested by receiving apparatus to provide data (exchanged key) for producing a key for decrypting a cryptogram, the number of receiving apparatus on which authentication is executed (authentication count) is limited to limit the number of receiving apparatus enabled to decrypt encrypted contents.
In Internet technology, a method of using time to live (TTL) is known as a means of limiting the reachable range of transmitted data. TTL represents the time for which a packet lives in IPv4, and corresponds to the number of relays in IPv6.
According to this method, the number of routers via which IP packets can be sent can be set by a value set in a TTL field in an IP packet header. (See, for example, Japanese Patent Laid-Open No. 2000-49852 (e.g., page 3, FIG. 7). The disclosure of this document is incorporated herein by reference in its entirety.)
If, for example, TTL is set to TTL=1 in a transmitting apparatus which transmits AV data, it is written into TTL=0 at the time of passage through a router provided in a home and this AV data is discarded in a router outside the home and cannot reach any unspecified receiving apparatus outside the home.
The above-described methods for preventing AV data from being limitlessly distributed to unspecified receiving apparatus outside a home have drawbacks described below.
First, the method of limiting the number of receiving apparatus to which contents are distributed in the DTCP system has a problem described below.
This method only limits the number of receiving apparatus without discrimination as to whether one receiving apparatus exists in or out of a home. In use of this method, therefore, the distribution to appliances in a home essentially permissible with no problem is limited when the limit number of appliances is reduced for the purpose of limiting the distribution to unspecified appliances outside the home. Conversely, when the limit number of appliances is increased to avoid limiting the distribution to appliances in the home, the distribution to appliances outside the home to be limited cannot be sufficiently limited.
Second, the method of limiting the number of passable routers by selecting the time to live has a problem described below.
In Internet technology, a device which transmits IP packets in a local network by temporarily encapsulating the IP packets and restores the IP packets by decapsulating the packets is known as a VPN (Virtual Private Network) device. The VPN device can connect a network in a home to a network outside the home, and the above-mentioned TTL value is not changed by passage through the VPN device. Therefore, the distribution to unspecified out-of-home appliances by the VPN device cannot be limited by using TTL.
Therefore, an object of the present invention is to provide a data use management system, a transmitting apparatus having a management function, a data use management method, and so on which are capable of executing the distribution of data to receiving apparatus in a home with no problem in practice while limiting the distribution of data for unspecified receiving apparatus outside the home.